Pulsed nuclear magnetic resonance (NMR) will be used to study nuclear spin relaxation, molecular diffusion, and molecular interactions in model membranes in thermotropic liquid crystals. Lateral diffusion rates of lipids in oriented lipid/D2O multilayers will be studied using techniques developed and applied previously. The effects of temperature, D2O concentration, membrane phase transitions and membrane phase separations on lipid lateral diffusion will be measured. Changes of lipid diffusion upon addition to the bilayers of cholesterol, proteins, spin labels, fluorophores, heavy metal ions, and drugs will be investigated. The relative diffusion rates of lipids and of the compounds added to the membranes will also be measured to obtain information on how large molecule diffusion in a membrane is related to lipid diffusion rates. Carbon-13 NMR will be applied to membranes to obtain information on structural changes accompanying phase transitions and the addition to membranes of cholesterol and drugs. Conventional Fourier transform NMR and the recently developed proton enhanced double resonance carbon-13 technique, which yields high resolution spectra in solids and membranes, will be utilized. Proton and deuteron nuclear spin relaxation in partially deuterated liquid crystals will be used to test theories of spin relaxation in liquid crystal phases. Deuteron line width and line shape studies will provide information on molecular conformation in mesophases. Data from the study will be relevant to membrane dynamics, lipid/drug interactions, health problems related to plasma membrane transport deficiencies, and theories of membrane and liquid crystal structures.